You mean make it a mold by pressing the part into the clay and then pouring the resin into that? I haven't done it, but have done some resin mold making. I think your problems would be:
1. your part will deform the mold some as you pull it out of the clay. Maybe cooling the clay a bit before removing the part might help. You'll still probably have problems digging the part out of the clay, leaving marks that'll have to be cleaned up on the resin part you make.
2. and this is the biggie: the resin heats up as it sets, that'll probably melt the clay some, further deforming the mold, and contaminating the part.
Itt IS tempting, though, as you can see a lot of good detail when you pull the part from the clay.
Gene Beaird,
Pearland, Texas